package com.zhentao.util;

import java.util.ArrayList;
import java.util.List;

/**
 * 解析树形数据工具类
 * <p>
 * 这个工具类可以解析对象成为树形结构
 */
public class TreeParser {

    public static <E extends TreeEntity<E>> List<E> getTreeList(String topId, List<E> entityList) {

        List<E> resultList = new ArrayList<>();

        //获取顶层元素集合
        String parentId;
        for (E entity : entityList) {
            parentId = entity.getParentId();
            if (parentId == null || topId.equals(parentId)) {
                resultList.add(entity);
            }
        }

        //获取每个顶层元素的子数据集合
        for (E entity : resultList) {
            entity.setChildren(getSubList(entity.getId(), entityList));
        }

        return resultList;
    }


    private static <E extends TreeEntity<E>> List<E> getSubList(String id, List<E> entityList) {
        List<E> childList = new ArrayList<>();
        String parentId;

        //子集的直接子对象
        for (E entity : entityList) {
            parentId = entity.getParentId();
            if (id.equals(parentId)) {
                childList.add(entity);
            }
        }

        //子集的间接子对象
        for (E entity : childList) {
            entity.setChildren(getSubList(entity.getId(), entityList));
        }

        //递归退出条件
        if (childList.size() == 0) {
            return null;
        }

        return childList;
    }


}